U.S. patent application number 12/097462 was filed with the patent office on 2009-09-17 for hydrophilic, composite, microporous membrane and its production method.
This patent application is currently assigned to TONEN CHEMICAL CORPORATION. Invention is credited to Kotaro Kimishima.
Application Number | 20090234032 12/097462 |
Document ID | / |
Family ID | 38163016 |
Filed Date | 2009-09-17 |
United States Patent
Application |
20090234032 |
Kind Code |
A1 |
Kimishima; Kotaro |
September 17, 2009 |
HYDROPHILIC, COMPOSITE, MICROPOROUS MEMBRANE AND ITS PRODUCTION
METHOD
Abstract
A hydrophilic, composite, microporous membrane having an anion
exchange group and a cation exchange group on the outer surface or
pore surface of a microporous, thermoplastic resin membrane
substrate has excellent water permeability, mechanical strength,
fine-particles-removing properties, anion-removing properties and
cation-removing properties.
Inventors: |
Kimishima; Kotaro;
(Kanagawa-ken, JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W., SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
TONEN CHEMICAL CORPORATION
Minato-ku, Tokyo
JP
|
Family ID: |
38163016 |
Appl. No.: |
12/097462 |
Filed: |
December 15, 2006 |
PCT Filed: |
December 15, 2006 |
PCT NO: |
PCT/JP2006/325024 |
371 Date: |
September 4, 2008 |
Current U.S.
Class: |
521/27 |
Current CPC
Class: |
Y02P 70/50 20151101;
B01D 2323/38 20130101; Y02E 60/10 20130101; C02F 1/44 20130101;
H01M 50/411 20210101; Y02E 60/50 20130101; B01D 67/0093 20130101;
C02F 1/441 20130101; C02F 1/444 20130101; H01M 8/1072 20130101;
B01D 2325/36 20130101; B01J 47/12 20130101; B01D 69/125 20130101;
B01D 2323/36 20130101; B01J 43/00 20130101; B01D 67/009 20130101;
B01D 69/127 20130101; B01D 2325/18 20130101 |
Class at
Publication: |
521/27 |
International
Class: |
C08J 5/20 20060101
C08J005/20 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 15, 2005 |
JP |
2005-362194 |
Dec 15, 2005 |
JP |
2005-362195 |
Claims
1. A hydrophilic, composite, microporous membrane having an anion
exchange group and a cation exchange group on the outer surface or
pore surface of a microporous, thermoplastic resin membrane
substrate.
2. The hydrophilic, composite, microporous membrane according to
claim 1, wherein the anion exchange group is any one of primary to
quaternary amino groups and heterocyclic amine groups.
3. The hydrophilic, composite, microporous membrane according to
claim 1, wherein the cation exchange group is a sulfonic acid group
or a carboxyl group.
4. A method for producing the hydrophilic, composite, microporous
membrane recited in claim 1, comprising the steps of
graft-polymerizing a microporous, thermoplastic resin membrane
substrate with an unsaturated glycidyl compound, and adding an
anion exchange group and a cation exchange group to an epoxy group
in the resultant polymer.
5. A method for producing the hydrophilic, composite, microporous
membrane recited in claim 1, comprising the steps of
graft-polymerizing a microporous, thermoplastic resin membrane
substrate with an anion-exchange-group-containing unsaturated
monomer and a cation-exchange-group-containing unsaturated
monomer.
6. A method for producing the hydrophilic, composite, microporous
membrane recited in claim 1, comprising the steps of (i)
graft-polymerizing a microporous, thermoplastic resin membrane
substrate with a unsaturated glycidyl compound, bonding an anion
exchange group to an epoxy group in the resultant polymer, and then
graft-polymerizing the anion-exchange-group-containing substrate
with a cation-exchange-group-containing unsaturated monomer, or
(ii) graft-polymerizing a microporous, thermoplastic resin membrane
substrate with an unsaturated glycidyl compound and a
cation-exchange-group-containing unsaturated monomer, and then
bonding an anion exchange group to an epoxy group in the resultant
polymer.
7. A method for producing the hydrophilic, composite, microporous
membrane recited in claim 1, comprising the steps of (i)
graft-polymerizing a microporous, thermoplastic resin membrane
substrate with an unsaturated glycidyl compound and an
anion-exchange-group-containing unsaturated monomer, and then
bonding a cation exchange group to an epoxy group in the resultant
polymer, (ii) graft-polymerizing a microporous, thermoplastic resin
membrane substrate with an unsaturated glycidyl compound, bonding a
cation exchange group to an epoxy group in the resultant polymer,
and then graft-polymerizing the resultant
cation-exchange-group-containing substrate with an
anion-exchange-group-containing unsaturated monomer.
8. A method for producing the hydrophilic, composite, microporous
membrane recited in claim 1, comprising the steps of
graft-polymerizing a microporous, thermoplastic resin membrane
substrate with an unsaturated glycidyl compound, bonding an anion
exchange group to an epoxy group in the resultant polymer, and then
subjecting the resultant anion-exchange-group-containing substrate
to a plasma gas treatment or a corona discharge treatment to form a
carboxyl group.
9. A method for producing the hydrophilic, composite, microporous
membrane recited in claim 1, comprising the steps of
graft-polymerizing a microporous, thermoplastic resin membrane
substrate with an anion-exchange-group-containing unsaturated
monomer, and then subjecting the resultant
anion-exchange-group-containing substrate to a plasma gas treatment
or a corona discharge treatment to form a carboxyl group.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a hydrophilic, composite,
microporous membrane and its production method, particularly to a
hydrophilic, composite, microporous membrane having anion exchange
groups and cation exchange groups and its production method.
BACKGROUND OF THE INVENTION
[0002] In a system for producing ultra-pure water for washing
semiconductors, etc., reverse osmosis filtration membranes,
ultrafiltration membranes, microfiltration membranes, etc. are used
to remove impurities. The system for producing ultra-pure water
generally comprises a pretreatment system, a primary
water-purifying system and a secondary water-purifying system
(sub-system). In the pretreatment system, suspending materials and
colloidal materials are removed from water by coagulation
sedimentation, ultrafiltration, microfiltration, etc. The
pretreated water is supplied to the primary water-purifying system
equipped with a reverse osmosis filtration membrane apparatus, an
ion exchange apparatus, a degassing apparatus, etc., to remove
almost all ion components and total organic carbons (TOC). TOC
contained in a trace amount in water supplied to the sub-system is
decomposed by oxidation in an ultraviolet-oxidizing apparatus, and
decomposition products are removed by the ion exchange apparatus.
Ultra-fine particles not removed by the ion exchange apparatus are
removed by the ultrafiltration filtration membrane apparatus.
[0003] Ultra-pure water thus produced is supplied to the use site
for washing semiconductors, etc. However, recent dramatic increase
in the degree of integration of semiconductors has made the
patterns and sizes of semiconductors smaller, so that slight
contamination in pipes and equipments from the sub-system to the
use site has become unnegligible. Thus proposed is the removal of
trace amounts of ions and fine particles immediately upstream of
the use site.
[0004] For instance, JP 8-89954 A proposes a system comprising a
module containing hollow, microporous membrane fibers having
high-molecular chains having ion exchange groups immediately
upstream of a use site. However, the hollow, microporous membrane
fibers of this reference have only one of an anion exchange group,
a cation exchange group and a chelate-forming group as an ion
exchange group. Because impurities at the use site, though in trace
amounts, cannot easily be identified, the module system of JP
8-89954 A cannot necessarily remove all impurities.
[0005] JP 9-141262 A proposes a filter system disposed immediately
upstream of a use site, the filter system comprising a module
containing a single-layer membrane, a module containing a laminate
membrane, or series-connected modules each containing a
single-layer membrane, which are properly selected from an
anion-exchange-group-having membrane, a
cation-exchange-group-having membrane, a
chelate-exchange-group-having membrane and an ultrafiltration
membrane, depending on components to be removed.
[0006] However, it is difficult to identify impurities immediately
upstream of the use site. To remove all impurities using the filter
system of JP 9-141262 A, it is necessary to use a module containing
all of the above membranes, or series-connect a large number of
modules each containing a single-layer membrane. This leads to
drastic decrease in water permeability. To cope with this problem,
a booster pump may be used, but it undesirably causes contamination
again.
OBJECT OF THE INVENTION
[0007] Accordingly, an object of this invention is to provide a
hydrophilic, composite, microporous membrane having excellent water
permeability, mechanical strength, fine-particles-removing
properties, anion-removing properties and cation-removing
properties, and its production method.
DISCLOSURE OF THE INVENTION
[0008] As a result of intense research in view of the above object,
the inventors have found that a hydrophilic, composite, microporous
membrane having excellent water permeability, mechanical strength,
fine-particles-removing properties, anion-removing properties and
cation-removing properties can be obtained by introducing an anion
exchange group and a cation exchange group onto the outer surface
or pore surface of a microporous, thermoplastic resin membrane
substrate. This invention has been completed based on such
finding.
[0009] Thus, the hydrophilic, composite, microporous membrane of
this invention has an anion exchange group and a cation exchange
group on the outer surface or pore surface of a microporous,
thermoplastic resin membrane substrate.
[0010] The anion exchange group is preferably any one of primary to
quaternary amino groups and heterocyclic amine groups, quaternary
amino group more preferably. The cation exchange group is
preferably a sulfonic acid group or a carboxyl group.
[0011] The first method for producing a hydrophilic, composite,
microporous membrane according to this invention comprises the
steps of graft-polymerizing a microporous, thermoplastic resin
membrane substrate with an unsaturated glycidyl compound, and then
bonding an anion exchange group and a cation exchange group to an
epoxy group in the resultant polymer. In a preferred example of the
first method, part of epoxy groups in the graft-polymerized,
unsaturated glycidyl compound are reacted with amine or ammonia,
and the unreacted epoxy group is reacted with sulfate and/or
sulfite.
[0012] The second method for producing a hydrophilic, composite,
microporous membrane according to this invention comprises the
steps of graft-polymerizing a microporous, thermoplastic resin
membrane substrate with an anion-exchange-group-containing
unsaturated monomer and a cation-exchange-group-containing
unsaturated monomer. In a preferred example of the second method,
the substrate is graft-polymerized with an
anion-exchange-group-containing unsaturated monomer, and then with
a cation-exchange-group-containing unsaturated monomer.
[0013] The third method for producing a hydrophilic, composite,
microporous membrane according to this invention comprises the
steps of (i) graft-polymerizing a microporous, thermoplastic resin
membrane substrate with an unsaturated glycidyl compound, bonding
an anion exchange group to an epoxy group in the resultant polymer,
and then graft-polymerizing the resultant
anion-exchange-group-containing substrate with a
cation-exchange-group-containing unsaturated monomer, or (ii)
graft-polymerizing a microporous, thermoplastic resin membrane
substrate with an unsaturated glycidyl compound and a
cation-exchange-group-containing unsaturated monomer, and then
bonding an anion exchange group to an epoxy group in the resultant
polymer.
[0014] The fourth method for producing a hydrophilic, composite,
microporous membrane according to this invention comprises the
steps of (i) graft-polymerizing a microporous, thermoplastic resin
membrane substrate with an unsaturated glycidyl compound and an
anion-exchange-group-containing unsaturated monomer, and then
bonding a cation exchange group to an epoxy group in the resultant
polymer, or (ii) graft-polymerizing a microporous, thermoplastic
resin membrane substrate with an unsaturated glycidyl compound,
bonding a cation exchange group to an epoxy group in the resultant
polymer, and then graft-polymerizing the resultant
cation-exchange-group-containing substrate with an
anion-exchange-group-containing unsaturated monomer.
[0015] The fifth method for producing a hydrophilic, composite,
microporous membrane according to this invention comprises the
steps of graft-polymerizing a microporous, thermoplastic resin
membrane substrate with an unsaturated glycidyl compound, bonding
an anion exchange group to an epoxy group in the resultant polymer,
and then subjecting the resultant anion-exchange-group-containing
substrate to a plasma gas treatment or a corona discharge treatment
to form a carboxyl group.
[0016] The sixth method for producing a hydrophilic, composite,
microporous membrane according to this invention comprises the
steps of graft-polymerizing a microporous, thermoplastic resin
membrane substrate with an anion-exchange-group-containing
unsaturated monomer, and then subjecting the resultant
anion-exchange-group-containing substrate to a plasma gas treatment
or a corona discharge treatment to form a carboxyl group.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[1] Substrate
[0017] The substrate of the hydrophilic, composite, microporous
membrane is a microporous, thermoplastic resin membrane.
[0018] (1) Thermoplastic Resins
[0019] The thermoplastic resins include polyolefin resins,
olefin-halogenated olefin copolymer resins, fluororesins,
polysulfone resins, polycarbonate resins, polyester resins,
polyamide resins, polyarylene ether resins, polyarylene sulfide
resins, etc. Among them, the polyolefin resins, the
olefin-halogenated olefin copolymer resins and the fluororesins are
preferable.
[0020] The polyolefin resins can be homopolymers or copolymers of
ethylene, propylene, butene-1, pentene-1,
hexene-1,4-methylpentene-1, octene, vinyl acetate, methyl
methacrylate, styrene, etc. The fluororesins can be polyvinylidene
fluoride, polytetrafluoroethylene,
tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers,
tetrafluoroethylene-hexafluoropropylene-perfluoropropyl vinyl ether
copolymers, tetrafluoroethylene-hexafluoropropylene copolymers,
ethylene-tetrafluoroethylene copolymers, etc.
[0021] The thermoplastic resins are preferably polyolefin resins,
more preferably polyethylene resins described below, because of
excellent mechanical strength. The polyethylene resins can be (a)
ultra-high-molecular-weight polyethylene, (b) polyethylene other
than the ultra-high-molecular-weight polyethylene, or (c) a mixture
of ultra-high-molecular-weight polyethylene with the other
polyethylene (polyethylene composition). In any case, the
polyethylene resins have mass-average molecular weight (Mw) of
preferably 1.times.10.sup.4 to 1.times.10.sup.7, more preferably
5.times.10.sup.4 to 15.times.10.sup.6, most preferably
1.times.10.sup.5 to 5.times.10.sup.6, though not particularly
critical.
[0022] (a) Ultra-High-Molecular-Weight Polyethylene
[0023] The ultra-high-molecular-weight polyethylene has Mw of
5.times.10.sup.5 or more. The ultra-high-molecular-weight
polyethylene can be an ethylene homopolymer, but also an
ethylene-.alpha.-olefin copolymer containing a small amount of
another .alpha.-olefin. The other .alpha.-olefins than ethylene are
preferably propylene, butene-1, pentene-1,
hexene-1,4-methylpentene-1, octene-1, vinyl acetate, methyl
methacrylate, and styrene. The Mw of the
ultra-high-molecular-weight polyethylene is preferably
5.times.10.sup.5 to 1.times.10.sup.7, more preferably
1.times.10.sup.6 to 15.times.10.sup.6, particularly
1.times.10.sup.6 to 5.times.10.sup.6.
[0024] (b) Polyethylene Other than Ultra-High-Molecular-Weight
Polyethylene
[0025] The polyethylene other than the ultra-high-molecular-weight
polyethylene has Mw of 1.times.10.sup.4 or more and less than
5.times.10.sup.5, being preferably high-density polyethylene,
medium-density polyethylene, branched low-density polyethylene and
linear low-density polyethylene, more preferably high-density
polyethylene. The polyethylene having Mw of 1.times.10.sup.4 or
more and less than 5.times.10.sup.5 can be not only an ethylene
homopolymer, but also a copolymer containing a small amount of
another .alpha.-olefin such as propylene, butene-1, hexene-1, etc.
Such copolymers are preferably produced using single-site
catalysts.
[0026] (c) Polyethylene Composition
[0027] The polyethylene composition is a mixture of
ultra-high-molecular-weight polyethylene having Mw of
5.times.10.sup.5 or more, and the other polyethylene having Mw of
1.times.10.sup.4 or more and less than 5.times.10.sup.5 (at least
one selected from the group consisting of high-density
polyethylene, medium-density polyethylene, branched low-density
polyethylene and linear low-density polyethylene). The
ultra-high-molecular-weight polyethylene and the other polyethylene
may be the same as above. The molecular weight distribution
[mass-average molecular weight/number-average molecular weight
(Mw/Mn)] of this polyethylene composition can be easily controlled
depending on applications. The polyethylene composition is
preferably a composition of the above ultra-high-molecular-weight
polyethylene and the above high-density polyethylene. The amount of
the ultra-high-molecular-weight polyethylene is preferably 1% or
more by mass, more preferably 2 to 50% by mass, based on 100% by
mass of the entire polyethylene composition.
[0028] (d) Molecular Weight Distribution Mw/Mn
[0029] Mw/Mn is a measure of the molecular weight distribution, and
the larger this value is, the wider the molecular weight
distribution is. The Mw/Mn of the polyethylene resin is preferably
5 to 300, more preferably 10 to 100, though not critical, when the
polyethylene resin is any one of (a)-(c) above. The Mw/Mn of the
polyethylene (homopolymer or ethylene-.alpha.-olefin copolymer) can
be properly controlled by a multi-stage polymerization method. The
Mw/Mn of the polyethylene composition can be properly controlled by
the molecular weights and mixing ratio of components.
[0030] (2) Desired Properties of Microporous, Thermoplastic Resin
Membrane
[0031] Though not particularly critical, the pore structure of the
microporous, thermoplastic resin membrane is preferably a
three-dimensional network structure (three-dimensionally and
irregularly connected network structure) to obtain excellent
fine-particles-removing properties and ion-removing properties. The
average pore size is preferably 0.005 to 0.5 .mu.m. When the
average pore size is less than 0.005 .mu.m, it is difficult to
introduce ion exchange groups (anion exchange group, cation
exchange group and chelate-forming group), resulting in low water
permeability after the ion exchange groups are introduced. When the
average pore size is more than 0.5 .mu.m, low
fine-particles-removing properties are obtained. The average pore
size is determined from a pore size distribution curve, which is
obtained by the measurement of a pore size distribution by mercury
intrusion porosimetry.
[0032] Though not critical, the air permeability (JIS P8117), which
is converted to the value at 20-.mu.m thickness, is preferably 30
to 400 sec/100 ml. When the air permeability is less than 30
sec/100 ml, the membrane has low mechanical strength and large pore
size, resulting in poor fine-particles-removing properties. When
the air permeability is more than 400 sec/100 ml, the membrane
having ion exchange groups introduced has low water permeability
and air permeability, unsatisfactory for practical applications.
Though not critical, the porosity is preferably 25 to 80%. When the
porosity is less than 25%, the membrane having ion exchange groups
introduced has low water permeability and air permeability. On the
other hand, the porosity of more than 80% provides low mechanical
strength. Though not critical, the pin puncture strength, which is
converted to the value at 20-.mu.m thickness, is preferably 1,000
mN (102 gf) or more.
[0033] (3) Production Method of Microporous, Thermoplastic Resin
Membrane
[0034] The production method of the above microporous,
thermoplastic resin membrane comprises, for instance, the steps of
(a) melt-blending the above thermoplastic resin and
membrane-forming solvent, (b) extruding the resultant resin
solution through a die lip, (c) cooling the resultant extrudate to
form a gel-like sheet, (d) stretching the gel-like sheet (first
stretching), (e) removing the membrane-forming solvent, (f) drying
the membrane, (g) stretching the dried membrane again (second
stretching), and (h) heat-treating the stretched membrane, though
not critical.
[0035] (a) Melt Blending
[0036] The melt blending is preferably conducted in the extruder.
The melt-blending methods are described in Japanese Patents 2132327
and 3347835.
[0037] (b) Extrusion
[0038] The melt-blended resin solution is extruded from the
extruder through a die. The extrusion method is described in
Japanese Patent 2132327.
[0039] (c) Formation of Gel-Like Sheet
[0040] An extrudate from the die is cooled to form a gel-like
sheet. The method for forming the gel-like sheet is described in
Japanese Patent 2132327.
[0041] (d) First Stretching
[0042] The gel-like sheet is stretched at least monoaxially. The
stretching causes cleavage between thermoplastic resin crystal
lamellas, making the thermoplastic resin phase finer with larger
numbers of fibrils. The fibrils form a three-dimensional network
structure (three-dimensionally and irregularly connected network
structure). Because the stretching method is described in Japanese
Patent 2132327, its detailed explanation will be omitted.
[0043] (e) Removal of Membrane-Forming Solvent
[0044] A washing solvent is used to remove (wash away) the
membrane-forming solvent. The methods for removing the
membrane-forming solvent with a washing solvent are described in
Japanese Patent 2132327 and JP 2002-256099 A.
[0045] (f) Drying of Membrane
[0046] The microporous, thermoplastic resin membrane obtained by
removing the membrane-forming solvent is then dried by a
heat-drying method, a wind-drying method, etc.
[0047] (g) Second Stretching
[0048] The dried membrane is preferably stretched again at least
monoaxially. The second stretching can be conducted by a tenter
method, etc., while heating the membrane. The second stretching may
be monoaxial or biaxial. In the case of biaxial stretching, both
simultaneous biaxial stretching and sequential stretching can be
used, though the simultaneous biaxial stretching is preferable.
[0049] The second stretching temperature is preferably in a range
from the crystal dispersion temperature Tcd of the
substrate-forming thermoplastic resin to (Tcd+40.degree. C.), more
preferably (Tcd+10.degree. C.) to (Tcd+40.degree. C.). The second
stretching temperature exceeding (Tcd+40.degree. C.) provides low
water permeability and air permeability, and large unevenness in
properties, particularly air permeability, in a sheet width
direction when stretched in a transverse direction (TD). The second
stretching temperature of lower than Tcd provides insufficient
softening of the thermoplastic resin, making it likely that
breakage occurs when the membrane is stretched, thus failing to
achieve uniform stretching. When the thermoplastic resin is a
polyethylene resin, the stretching temperature is usually in a
range from 90.degree. C. to 140.degree. C., preferably in a range
from 100.degree. C. to 130.degree. C.
[0050] The second stretching magnification is preferably 1.1 to
2.5-fold in one direction. In the case of monoaxial stretching, it
is 1.1 to 2.5-fold in a longitudinal direction (MD) or in TD. In
the case of biaxial stretching, it is 1.1 to 2.5-fold in both MD
and TD. In the case of biaxial stretching, the stretching
magnifications in MD and TD may be the same or different, as long
as they are 1.1 to 2.5-fold, although they are preferably the same.
The magnification of less than 1.1-fold provides insufficient water
permeability and air permeability. On the other hand, the
magnification of more than 2.5-fold makes the breakage of the
membrane highly likely and provides undesirably low heat shrinkage
resistance. The second stretching magnification is more preferably
1.1 to 2.0-fold.
[0051] The second stretching speed is preferably 3%/second or more
in a stretching direction. In the case of monoaxial stretching, it
is 3%/second or more in MD or TD. In the case of biaxial
stretching, it is 3%/second or more in both MD and TD. The
stretching speed (%/second) in a stretching direction is a
percentage of the elongation of the membrane in a second stretching
region per 1 second relative to the length (100%) before the second
stretching. The stretching speed of less than 3%/second provides
low water permeability and air permeability, and large unevenness
in properties, particularly air permeability, in a sheet width
direction in the stretching in TD. The second stretching speed is
preferably 5%/second or more, more preferably 10%/second or more.
In the case of biaxial stretching, the stretching speed may be
different in MD and TD as long as it is 3%/second or more in each
of MD and TD, though the same stretching speed is preferable.
Though not critical, the upper limit of the second stretching speed
is preferably 50%/second to prevent the breakage of the
membrane.
[0052] (h) Heat Treatment
[0053] The membrane after second stretching is preferably
heat-treated. The heat treatment may be heat-setting and/or
annealing. These methods are described, for instance, in JP
2002-256099 A.
[0054] (i) Other Steps
[0055] Before removing the membrane-forming solvent from the
gel-like sheet, any one of a heat-setting step, a hot roll
treatment step, in which the stretched gel-like sheet is brought
into contact with at least one surface of a hot roll, and a hot
solvent treatment step, in which the stretched gel-like sheet is
brought into contact with a hot solvent, can be conducted. The
heat-setting treatment can be conducted by the above known method.
The hot roll treatment can be conducted by the method described in
Japanese Application 2005-271046. The hot solvent treatment can be
conducted by the method described in WO 2000/20493.
[0056] [2] Ion Exchange Groups
[0057] The hydrophilic, composite, microporous membrane has an
anion exchange group and a cation exchange group on the outer
surface or pore surface of the above microporous, thermoplastic
resin membrane substrate. The hydrophilic, composite, microporous
membrane preferably has both ion exchange groups on both outer
surface and pore surface of the substrate.
[0058] (1) Anion Exchange Group
[0059] The anion exchange group is preferably any one of primary
amino groups represented by the formula (1):
--NH.sub.2 (1),
secondary amino groups represented by the formula (2):
##STR00001##
wherein R.sup.1 is a hydrocarbon group, tertiary amino groups
represented by the formula (3):
##STR00002##
wherein R.sup.2 and R.sup.3 are hydrocarbon groups, quaternary
amino groups represented by the formula (4):
##STR00003##
wherein R.sup.4 to R.sup.6 are hydrocarbon groups, and heterocyclic
amine groups such as pyridines, imidazoles, etc., more preferably
strongly basic quaternary amino groups. The hydrocarbon groups
(R.sup.1 to R.sup.6) in the secondary to quaternary amino groups
can be any one of alkyl groups, aryl groups and aralkyl groups.
[0060] The amount of the anion exchange group is preferably 0.1
milliequivalent or more, more preferably 0.2 milliequivalent or
more, per 1 g of the hydrophilic, composite, microporous membrane.
When this amount is less than 0.1 milliequivalent/g, insufficient
anion-removing properties are obtained.
[0061] (2) Cation Exchange Group
[0062] The cation exchange group can be a sulfonic acid group, a
carboxyl group, a phosphorus-containing acid group (for instance, a
phosphoric acid group, a phosphonic acid group, etc.), etc.,
preferably a sulfonic acid group and a carboxyl group. The amount
of the cation exchange group is preferably 0.1 milliequivalent or
more, more preferably 0.2 milliequivalent or more, per 1 g of the
hydrophilic, composite, microporous membrane. When this amount is
less than 0.1 milliequivalent/g, insufficient cation-removing
properties are obtained.
[0063] (3) Ratio of Anion Exchange Group to Cation Exchange
Group
[0064] The ratio of the anion exchange group to the cation exchange
group can properly be determined depending on the components to be
removed, but the anion exchange group/cation exchange group molar
ratio is preferably 10/90 to 90/10, more preferably 20/80 to
80/20.
[0065] (4) Chelate-Forming Group
[0066] The hydrophilic, composite, microporous membrane can have a
chelate-forming group, as the other ion exchange group than the
anion exchange group and the cation exchange group, if necessary.
The chelate-forming group is a functional group forming a chelate
with a metal ion. The chelate-forming group includes an
iminodiacetate group, a mercapto group, an ethylenediamine group,
etc. The ratio of the chelate-forming group is preferably 20% by
mol or less per 100% by mol of all the ion exchange groups.
[0067] (5) Total Amount of Ion Exchange Groups
[0068] The total amount of the ion exchange groups (anion exchange
group+cation exchange group+chelate-forming group) is preferably 10
milliequivalent or less, more preferably 5 milliequivalent or less,
per 1 g of the hydrophilic, composite, microporous membrane. When
this amount is more than 10 milliequivalent/g, pores are likely to
close.
[0069] [3] Production Method of Hydrophilic, Composite, Microporous
Membrane
[0070] The method for producing a hydrophilic, composite,
microporous membrane comprises the steps of (1) introducing the
anion exchange group and the cation exchange group into the above
microporous, thermoplastic resin membrane substrate, (2) washing
it, and (3) drying it. When the tertiary amino group is introduced
in the step (1), a step (4) of turning the tertiary amino group to
a quaternary one is preferably conducted after the step (1). After
the step (1) (before the step (4), if any), a step (5) of
introducing a chelate-forming group can be conducted, if
necessary.
[0071] (1) Introduction of Anion Exchange Group and Cation Exchange
Group
[0072] (1)-1 Method of Introducing Anion Exchange Group
[0073] The introduction of the anion exchange group into the
substrate can be conducted by (a) a method comprising
graft-polymerizing the substrate with an unsaturated glycidyl
compound, and reacting amine or ammonia with an epoxy group in the
resultant polymer (first method of introducing an anion exchange
group), and (b) a method comprising graft-polymerizing the
substrate with an anion-exchange-group-containing unsaturated
monomer (second method of introducing an anion exchange group).
[0074] (a) First Method of Introducing Anion Exchange Group
[0075] (i) Graft Polymerization of Unsaturated Glycidyl
Compound
[0076] The graft polymerization of the substrate with an
unsaturated glycidyl compound can be conducted by a method
comprising irradiating the substrate with ionizing radiation, and
then reacting the substrate with an unsaturated glycidyl compound
(prior-irradiation method), and a method of irradiating ionizing
radiation to the substrate in contact with the unsaturated glycidyl
compound (simultaneous irradiation method). Because the ionizing
radiation penetrates into the substrate, the unsaturated glycidyl
compound is polymerized to form side chains substantially uniformly
connected to main chains of the thermoplastic resin on the outer
surface and pore surface of the substrate. The ionizing radiation
includes .alpha.-rays, .beta.-rays (electron beams), .gamma.-rays
and X-rays, and electron beams and .gamma.-rays are preferable for
handling. In the case of using electron beams, the
prior-irradiation method is preferable to suppress the
homopolymerization of the unsaturated glycidyl compound.
[0077] When the electron beam treatment is conducted by the
prior-irradiation method, the acceleration voltage of electron
beams is preferably 100 to 5,000 keV, more preferably 1,000 to
4,000 keV. The irradiation of electron beams can be conducted in an
air atmosphere, but preferably in an inert gas atmosphere. The
amount of irradiation is 10 to 500 kGy, preferably 50 to 200 kGy.
When the amount of irradiation is less than 10 kGy, the unsaturated
glycidyl compound is not sufficiently grafted. When the amount of
irradiation exceeds 500 kGy, the substrate is likely
deteriorated.
[0078] The substrate having radicals generated by the irradiation
of electron beams is brought into contact with an unsaturated
glycidyl compound in a gas or liquid state. The unsaturated
glycidyl compound is not particularly restricted as long as it is a
compound having a glycidyl group and an unsaturated group, but it
is preferably glycidyl(meth)acrylic acid. The contact of the
substrate with an unsaturated glycidyl compound in a gas state can
be conducted by a method comprising bubbling the evaporated
unsaturated glycidyl compound in a solvent, in which the irradiated
substrate is immersed (gas method). The contact of the substrate
with an unsaturated glycidyl compound in a liquid state can be
conducted by a method comprising immersing the irradiated substrate
in a solution or dispersion of the unsaturated glycidyl compound
(liquid method). In any method, water and an organic solvent can be
used, but the organic solvent is preferable. The preferred organic
solvents are lower alcohols such as methanol, ethanol, isopropyl
alcohol (IPA), butanol, etc. A surfactant can be added to the
solution or dispersion of the unsaturated glycidyl compound, if
necessary.
[0079] The concentration of the solution or dispersion of the
unsaturated glycidyl compound is preferably 0.1 to 20% by mass,
more preferably 0.5 to 10% by mass. When this concentration is less
than 0.1% by mass, it is impossible to graft-polymerize the
substrate with a sufficient amount of the unsaturated glycidyl
compound. When the concentration is more than 20% by mass, it is
difficult to control the amount of polymerization. The solution or
dispersion of the unsaturated glycidyl compound is preferably
deoxidized before the immersion of the substrate. The deoxidation
can be conducted by bubbling an inert gas. An inert gas can be
bubbled while the substrate is immersed, if necessary. The
immersion temperature is preferably 0 to 90.degree. C., more
preferably 20 to 70.degree. C. The treatment time is about 10 to 60
minutes, for instance, at 50.degree. C., though different depending
on the immersion temperature.
[0080] The unsaturated glycidyl compound can be graft-polymerized
in the presence of a cross-linking agent, if necessary. The
cross-linking agent is divinyl benzene, etc. To prevent the
homopolymerization of the unsaturated glycidyl compound, a
polymerization inhibitor such as Mohr's salt [iron(II) ammonium
sulfate-hexahydrate] and hydroquinone monomethyl ether, IPA,
ethylene dichloride, etc. can be used.
[0081] The graft ratio of the unsaturated glycidyl compound is,
preferably 5 to 100% by mass, more preferably 10 to 50% by mass,
based on 100% by mass of the ungrafted substrate.
[0082] (ii) Introduction of Anion Exchange Group
[0083] The anion exchange group is bonded to an epoxy group in the
polymer of the unsaturated glycidyl compound (side chains).
Specifically, amine or ammonia is reacted with the epoxy group to
form any one of primary to tertiary amino groups. It is preferable
to use an amine to form a secondary or tertiary amino group. To
form the quaternary amino group, a tertiary amino group is formed
and then turned to a quaternary one. The formation of a quaternary
amino group is preferably conducted after the cation exchange group
is introduced.
[0084] The amines include aliphatic amines, aromatic amines,
alicyclic amines, aliphatic hydroxylamines, aliphatic diamines,
aromatic diamines, heterocyclic amines, etc., and aliphatic amines
and heterocyclic amines are preferable from the aspect of basicity.
The aliphatic amines are, for instance, methylamine, dimethylamine,
ethylamine, diethylamine, n-propylamine, di-n-propylamine,
n-butylamine, di-n-butylamine, n-amylamine, n-hexylamine,
laurylamine, etc. The heterocyclic amines are, for instance,
pyridine, imidazole, etc. They may be used alone or in
combination.
[0085] To react the epoxy group with the amine, it is preferable to
immerse the substrate provided with side chains in an amine
solution or dispersion. The solvent may be any one of water,
organic solvents and mixtures thereof.
[0086] Among them, a water-lower alcohol mixed solvent is
preferable. The amount of the amine introduced can be controlled by
adjusting the concentration of the amine in the solution or
dispersion, the immersion temperature and the treatment time.
Though not critical, the amine concentration is preferably 0.5 to
15% by mass. The immersion temperature is preferably 0 to
90.degree. C., more preferably 20 to 70.degree. C. The treatment
time is about 30 minutes to 2 hours, for instance, at 50.degree.
C., though different depending on the immersion temperature.
[0087] (b) Second Method of Introducing an Anion Exchange Group
[0088] The second method comprises irradiating the substrate with
ionizing radiation like the above, bringing an
anion-exchange-group-containing unsaturated monomer into contact
with the substrate to cause graft polymerization. The
anion-exchange-group-containing unsaturated monomers include vinyl
pyridine, vinyl imidazole, diallylmethylamine, allylamine, N,
N-dimethyl-p-amino styrene, N,N-diethyl-p-amino styrene, vinyl
amine, N, N-dimethylamino methyl(meth)acrylate,
N,N-diethylaminomethyl (meth)acrylate,
N,N-dimethylaminoethyl(meth)acrylate, N,
N-diethylaminoethyl(meth)acrylate, etc.
[0089] The contact of the substrate with an
anion-exchange-group-containing unsaturated monomer can be
conducted by the gas method or the liquid method. In the case of
the liquid method, the same solvent, monomer concentration,
immersion temperature and treatment time can be used as in the case
of graft-polymerizing the unsaturated glycidyl compound.
[0090] (1)-2 Method of Introducing Cation Exchange Group
[0091] (a) Method of Introducing Sulfonic Acid Group
[0092] The method of introducing a sulfonic acid group into the
substrate includes (i) a method comprising graft-polymerizing the
substrate with an unsaturated glycidyl compound, and reacting an
epoxy group in the resultant polymer with a sulfate or a sulfite
(first method of introducing sulfonic acid group), and (ii) a
method comprising graft-polymerizing the substrate with a
sulfonic-acid-group-containing unsaturated monomer (second method
of introducing sulfonic acid group).
[0093] (i) First Method of Introducing Sulfonic Acid Group
[0094] The first method comprises graft-polymerizing the substrate
with an unsaturated glycidyl compound like the above, reacting an
epoxy group in the resultant polymer (side chains) with sulfate or
sulfite [simply called "sulfate (sulfite)"]. The sulfates include
alkali metal sulfates such as sodium sulfate, potassium sulfate,
etc. The sulfites include alkali metal sulfites such as sodium
sulfite and potassium sulfite, magnesium sulfite, sodium hydrogen
sulfite, potassium hydrogen sulfite, ammonium sulfite, etc. They
may be used alone or in combination.
[0095] To react the sulfate (sulfite) with the epoxy group, it is
preferable to immerse the substrate provided with side chains in a
solution or dispersion of the sulfate (sulfite). The solvent may be
the same as shown in the reaction with the amine. The concentration
of the sulfate (sulfite) in the solution or dispersion is
preferably 0.5 to 10% by mass. The immersion temperature is
preferably 0 to 100.degree. C., more preferably 20 to 90.degree. C.
The treatment time is about 10 to 20 hours, for instance, at
80.degree. C., though different depending on the immersion
temperature. A sulfonic acid group can be formed by reacting the
epoxy group with the sulfate (sulfite), and treating it by
hydrochloric acid, etc. to ion-exchange the alkali metal, etc. to a
proton.
[0096] (ii) Second Method of Introducing Sulfonic Acid Group
[0097] The second method comprises irradiating the substrate with
ionizing radiation like the above, and graft-polymerizing it with a
sulfonic-acid-group-containing unsaturated monomer. The
sulfonic-acid-group-containing unsaturated monomers include vinyl
sulfonic acid, p-styrene sulfonic acid, allyl sulfonic acid,
methallyl sulfonic acid, butyl (meth)acrylate-4-sulfonic acid,
(meth)acryloxybenzene sulfonic acid, t-butylacrylamide sulfonic
acid, etc. They may be used alone or in combination.
[0098] The contact of the substrate with the
sulfonic-acid-group-containing unsaturated monomer can be conducted
by the gas method or the liquid method. In the case of the liquid
method, the same solvent, monomer concentration, immersion
temperature and treatment time can be used as in the graft
polymerization of the unsaturated glycidyl compound.
[0099] (b) Method of Introducing Carboxyl Group
[0100] The method of introducing a carboxyl group into the
substrate includes (i) a method comprising graft-polymerizing the
substrate with an unsaturated glycidyl compound, reacting an epoxy
group in the resultant polymer with either an alkali
metal-aliphatic acid salt or alkali metal hydroxycarboxylate (first
method of introducing a carboxyl group), (ii) a method comprising
graft-polymerizing the substrate with a carboxyl group-containing
unsaturated monomer (second method of introducing a carboxyl
group), and (iii) a method comprising subjecting the substrate to a
plasma gas treatment or a corona discharge treatment (third method
of introducing a carboxyl group).
[0101] (i) First Method of Introducing Carboxyl Group
[0102] The first method comprises graft-polymerizing the substrate
with an unsaturated glycidyl compound like the above, and reacting
an epoxy group in the resultant polymer (side chains) with any one
of alkali metal-aliphatic acid salts and alkali metal
hydroxycarboxylates. The alkali metal-aliphatic acid salts include
sodium acetate, sodium propionate, sodium butyrate, sodium
caproate, sodium caprylate, sodium caprate, sodium laurate, sodium
myristate, sodium palmitate, sodium stearate, etc. The alkali metal
hydroxycarboxylates include sodium glycolate, sodium lactate,
sodium malate, sodium tartrate, sodium citrate, sodium gluconate,
etc. They may be used alone or in combination.
[0103] To react the epoxy group with any one of the alkali
metal-aliphatic acid salts and the alkali metal
hydroxycarboxylates, the substrate graft-polymerized with the
unsaturated glycidyl compound is preferably immersed in a solution
or dispersion of either the alkali metal-aliphatic acid salt or the
alkali metal hydroxycarboxylate. The same solvent can be used as in
the reaction with the amine. The concentration of the salt in the
solution or dispersion is preferably 0.5 to 10% by mass. The
immersion temperature is preferably 0 to 100.degree. C., more
preferably 20 to 90.degree. C. The treatment time is about 10 to 20
hours, for instance, at 80.degree. C., though different depending
on the immersion temperature. After the epoxy group is reacted with
the alkali metal-aliphatic acid salt and/or the alkali metal
hydroxycarboxylate, the substrate can be treated with hydrochloric
acid, etc. to ion-exchange the alkali metal to a proton, thereby
forming a carboxyl group.
[0104] (ii) Second Method of Introducing Carboxyl Group
[0105] The second method comprises irradiating the substrate with
ionizing radiation like the above, and graft-polymerizing it with a
carboxyl group-containing unsaturated monomer. The carboxyl
group-containing unsaturated monomers include unsaturated, mono- or
di-carboxylic acids such as (meth)acrylic acid, maleic acid,
fumaric acid, endo-bicyclo[2.2.1]-5-heptene-2,3-dicarboxylic acid
(endic acid), tetrahydrophthalic acid, itaconic acid, citraconic
acid, crotonic acid and isocrotonic acid, and their derivatives,
etc. Such derivatives are, for instance, anhydrides, halides,
amides, imides, esters, etc. Specific examples of the derivatives
are maleic anhydride, maleinyl chloride, maleimide, endic
anhydride, methyl acrylate, methyl methacrylate, citraconic
anhydride, monomethyl maleate, dimethyl maleate, etc. They may be
used alone or in combination. Among them, (meth)acrylic acid is
preferable.
[0106] The contact of the substrate with an carboxyl
group-containing unsaturated monomer can be conducted by the gas
method or the liquid method. In the case of the liquid method, the
same solvent, monomer concentration, immersion temperature and
treatment time can be used as in the graft polymerization of the
unsaturated glycidyl compound.
[0107] (iii) Third Method of Introducing Carboxyl Group
[0108] The third method comprises subjecting the substrate to a
plasma gas treatment or a corona discharge treatment to form a
carboxyl group. Using a known a plasma gas generating apparatus,
the plasma gas treatment can be conducted by exposing the substrate
to a plasma gas. A plasma-generating gas is argon, helium,
nitrogen, air, etc. High-frequency current for generating the
plasma gas preferably has a frequency of 1 to 30 MHz, and output of
1 to 5,000 W, more preferably 100 to 3,000 W. The plasma gas is
blown onto the substrate at a flow rate of preferably 0.002 to 2
L/min/cm.sup.2, more preferably 0.02 to 1.2 L/min/cm.sup.2.
[0109] Using a known corona discharge apparatus, the corona
discharge treatment is conducted by exposing the substrate to a
corona atmosphere generated. The corona discharge treatment is
preferably conducted in an air atmosphere. The total amount of
discharge in the corona discharge treatment is preferably 1 to
5,000 W/m.sup.2/min, more preferably 100 to 3,000 W/m.sup.2/min.
The pressure in the plasma gas treatment and the corona discharge
treatment can be atmospheric pressure, and the treatment time is
preferably 1 to 1,000 seconds.
[0110] (1)-3 Combinations of these Methods
[0111] The above anion-exchange-group-introducing method,
sulfonic-acid-group-introducing method and
carboxyl-group-introducing method can be properly combined to
introduce any one of the anion exchange group, the sulfonic acid
group and carboxyl group into the substrate.
[0112] (a) Introduction of Anion Exchange Group and Sulfonic Acid
Group
[0113] The introduction of the anion exchange group and the
sulfonic acid group into the substrate can be conducted by a
combination A of the first anion-exchange-group-introducing method
and the first sulfonic-acid-group-introducing method, a combination
B of the second anion-exchange-group-introducing method and the
second sulfonic-acid-group-introducing method, a combination C of
the first anion-exchange-group-introducing method and the second
sulfonic-acid-group-introducing method, and a combination D of the
second anion-exchange-group-introducing method and the first
sulfonic-acid-group-introducing method. Among them, the combination
A is preferable.
[0114] (i) Combination A
[0115] The combination A comprises the steps of graft-polymerizing
the substrate with the unsaturated glycidyl compound, and bonding
the anion exchange group and the sulfonic acid group to an epoxy
group in the resultant polymer. Though not critical, the anion
exchange group and the sulfonic acid group are introduced
preferably in this order. Namely, after part of epoxy group in the
polymer of the unsaturated glycidyl compound is reacted with the
amine or ammonia, the unreacted epoxy group is preferably reacted
with the sulfate (sulfite), and then ion-exchanged. When the
sulfonic acid group is first introduced, or when the amine or
ammonia and the sulfate (sulfite) are simultaneously reacted with
the epoxy group, the addition reaction of the amine or ammonia is
hindered, resulting in difficulty in introducing the anion exchange
group.
[0116] (ii) Combination B
[0117] The combination B comprises graft-polymerizing the substrate
with the anion-exchange-group-containing unsaturated monomer and
the sulfonic-acid-group-containing unsaturated monomer. Though not
critical, to graft-polymerize both monomers in good balance, the
anion-exchange-group-containing unsaturated monomer and the
sulfonic-acid-group-containing unsaturated monomer are
graft-polymerized preferably in this order. If necessary, however,
the graft polymerization may be conducted in an opposite order, or
both monomers may be graft-copolymerized.
[0118] When the graft polymerization of the
anion-exchange-group-containing unsaturated monomer and the graft
polymerization of the sulfonic-acid-group-containing unsaturated
monomer are conducted by separate steps, it is preferable to
conduct irradiation before each graft polymerization step. To
suppress the deterioration of the substrate and the degradation of
the previously introduced ion exchange group, the amount of
irradiation is properly controlled. Specifically, the amount of
irradiation is preferably 50 to 200 kGy. The acceleration voltage
of electron beams may be the same as above. In the combination
conducting irradiation plural times, the amount of each irradiation
is preferably the same as above.
(iii) Combination C
[0119] The combination C includes a combination C-1 comprising
graft-polymerizing the substrate with an unsaturated glycidyl
compound, bonding an anion exchange group to an epoxy group in the
resultant polymer, and then graft-polymerizing the resultant
anion-exchange-group-containing substrate with a
sulfonic-acid-group-containing unsaturated monomer, and a
combination C-2 comprising graft-polymerizing the substrate with an
unsaturated glycidyl compound and a sulfonic-acid-group-containing
unsaturated monomer, and then bonding an anion exchange group to an
epoxy group in the resultant polymer.
[0120] In the combination C-1, irradiation is preferably conducted
before each graft polymerization. In the combination C-2, the
irradiated substrate may be graft-copolymerized with an unsaturated
glycidyl compound and a sulfonic-acid-group-containing unsaturated
monomer, or graft-polymerized with an unsaturated glycidyl compound
and a sulfonic-acid-group-containing unsaturated monomer in this
order. The former graft copolymerization method may be essentially
the same as the method of graft-polymerizing only the unsaturated
glycidyl compound. In the latter sequential graft polymerization,
irradiation is preferably conducted before the graft polymerization
of the sulfonic-acid-group-containing unsaturated monomer.
[0121] (iv) Combination D
[0122] The combination D includes a combination D-1 comprising
graft-polymerizing the substrate with an unsaturated glycidyl
compound and an anion-exchange-group-containing unsaturated
monomer, and then bonding a sulfonic acid group to an epoxy group
in the resultant polymer, and a combination D-2 comprising
graft-polymerizing the substrate with an unsaturated glycidyl
compound, bonding a sulfonic acid group to an epoxy group in the
resultant polymer, and then graft-polymerizing the
sulfonic-acid-group-containing substrate with an
anion-exchange-group-containing unsaturated monomer.
[0123] In the combination D-1, the irradiated substrate may be
graft-copolymerized with an unsaturated glycidyl compound and an
anion-exchange-group-containing unsaturated monomer, or
graft-polymerized with an unsaturated glycidyl compound and an
anion-exchange-group-containing unsaturated monomer in this order.
The former graft copolymerization method may be essentially the
same as the method of graft-polymerizing only the unsaturated
glycidyl compound. In the latter sequential graft polymerization,
irradiation is preferably conducted before the graft polymerization
of the anion-exchange-group-containing unsaturated monomer. In the
combination D-2, irradiation is preferably conducted before each
graft polymerization.
[0124] (b) Introduction of Anion Exchange Group and Carboxyl
Group
[0125] The introduction of the anion exchange group and the
carboxyl group into the substrate can be conducted by a combination
E of the first anion-exchange-group-introducing method and the
first carboxyl-group-introducing method, a combination F of the
second anion-exchange-group-introducing method and the second
carboxyl-group-introducing method, a combination G of the first
anion-exchange-group-introducing method and the second
carboxyl-group-introducing method, a combination H of the second
anion-exchange-group-introducing method and the first
carboxyl-group-introducing method, a combination I of the first
anion-exchange-group-introducing method and the third
carboxyl-group-introducing method, and a combination J of the
second anion-exchange-group-introducing method and the third
carboxyl-group-introducing method. Among them, the combination G, I
or J is preferable.
[0126] The combinations E and H may be the same as the combinations
A and D, respectively, except that the carboxyl group is introduced
in place of the sulfonic acid group [either the alkali
metal-aliphatic acid salt or the alkali metal hydroxycarboxylate in
place of the sulfate (sulfite) is reacted with the epoxy
group].
[0127] The combinations F and G may be the same as the combinations
B and C, respectively, except that the carboxyl group is introduced
in place of the sulfonic acid group (the carboxyl group-containing
unsaturated monomer is graft-polymerized in place of the
sulfonic-acid-group-containing unsaturated monomer).
[0128] The combination I comprises the steps of graft-polymerizing
the substrate with an unsaturated glycidyl compound, bonding an
anion exchange group to an epoxy group in the resultant polymer,
and subjecting the resultant anion-exchange-group-containing
substrate to a plasma gas treatment or a corona discharge treatment
to form a carboxyl group. These steps may be the same as above.
[0129] The combination J comprises graft-polymerizing the substrate
with an anion-exchange-group-containing unsaturated monomer, and
subjecting the resultant anion-exchange-group-containing substrate
to a plasma gas treatment or a corona discharge treatment to form a
carboxyl group. These steps may be the same as above.
[0130] (c) Introduction of Anion Exchange Group, Sulfonic Acid
Group and Carboxyl Group
[0131] When the anion exchange group, the sulfonic acid group and
the carboxyl group are introduced into the substrate, the first
anion-exchange-group-introducing method, the first
sulfonic-acid-group-introducing method and the third
carboxyl-group-introducing method are preferably combined, though
not critical. Specifically, a step of graft-polymerizing the
substrate with an unsaturated glycidyl compound, a step of bonding
an anion exchange group and a sulfonic acid group to an epoxy group
in the resultant polymer, and a step of subjecting the substrate
containing the anion exchange group and the sulfonic acid group to
a plasma gas treatment or a corona discharge treatment to form a
carboxyl group are preferably conducted in this order. These steps
may be the same as above.
[0132] (2) Washing
[0133] The substrate having the anion exchange group and the cation
exchange group introduced is washed with a solvent such as water,
toluene, xylene, etc. overnight.
[0134] (3) Drying
[0135] The washed membrane is dried by a heat-drying method, an
air-drying method, etc., to obtain a hydrophilic, composite,
microporous membrane.
[0136] (4) Turning to Quaternary Amine
[0137] When the tertiary amino group is introduced by the above
anion-exchange-group-introducing method, it is preferable to turn
the tertiary amino group to a quaternary one, a stronger basic
group, before washing and drying. To turn the tertiary amino group
to a quaternary one, the tertiary amino group is reacted with
halogenated aryl, chlorohydrin, halogenated alkyl, etc. The
halogenated aryl is preferably halogenated benzyl such as benzyl
chloride, etc. The chlorohydrin is ethylene chlorohydrin, propylene
chlorohydrin, etc. These halides may be used alone or in
combination. The method of turning the tertiary amino group to a
quaternary one preferably comprises immersing the substrate having
the tertiary amino group and the cation exchange group in a
solution or dispersion of the above halide. The same solvent can be
used as in the preparation of the amine solution. The concentration
of the halide in the solution or dispersion is preferably 0.5 to
20% by mass. The immersion temperature is preferably 0 to
100.degree. C., more preferably 20 to 90.degree. C. The treatment
time is about 10 to 50 hours, for instance, at 80.degree. C.,
though different depending on the immersion temperature. The
membrane formed with the quaternary amino group is dried like the
above washing.
[0138] (5) Introduction of Chelate-Forming Group
[0139] The chelate-forming group can be introduced, if necessary.
The chelate-forming group is introduced after the anion exchange
group and the cation exchange group is introduced into the
substrate, and before the tertiary amino group is turned to a
quaternary one. To introduce the chelate-forming group, the
membrane is immersed in a solution or dispersion of sodium
iminodiacetate, etc., such that it can be reacted with an unreacted
epoxy group in the polymer of the unsaturated glycidyl
compound.
[0140] [4] Properties of Hydrophilic, Composite, Microporous
Membrane
[0141] The above production method provides a hydrophilic,
composite, microporous membrane having a good balance of an anion
exchange group and a cation exchange group on the outer surface and
pore surface of the microporous, thermoplastic resin membrane
substrate, with a three-dimensional network structure. The
hydrophilic, composite, microporous membrane according to a
preferred embodiment of this invention has the following
properties.
[0142] (1) Average Pore Size of 0.005 to 0.5 .mu.m
[0143] The average pore size of less than 0.005 .mu.m provides low
water permeability, and that of more than 0.5 .mu.m provides low
fine-particles-removing properties.
[0144] (2) Air Permeability of 30 to 400 sec/100 cm.sup.3
(converted to the value at 20-.mu.m thickness)
[0145] When the air permeability (JIS P8117) converted to the value
at 20-.mu.m thickness is 30 to 400 sec/100 cm.sup.3, the
hydrophilic, composite, microporous membrane exhibits good water
permeability when used as a water-treating membrane (water-treating
reverse osmosis filtration membrane, ultrafiltration membrane,
microfiltration membrane, etc.).
[0146] (3) Porosity of 25 to 80%
[0147] With the porosity of less than 25%, the hydrophilic,
composite, microporous membrane does not have good water
permeability and air permeability. When the porosity exceeds 80%,
the hydrophilic, composite, microporous membrane has low mechanical
strength.
[0148] (4) Pin Puncture Strength of 1,000 mN/20 .mu.m or More
[0149] With the pin puncture strength of less than 1,000 mN/20
.mu.m, the hydrophilic, composite, microporous membrane used as a
water-treating membrane has low durability.
[0150] As described above, the hydrophilic, composite, microporous
membrane has excellent mechanical strength and water permeability.
Further, the hydrophilic, composite, microporous membrane has
excellent capability of removing fine particles (fine metal oxide
particles, etc.), anions (inorganic acid ions, etc.), and cation
(metal ions, etc.). The hydrophilic, composite, microporous
membrane having such properties is suitable as a water-treating
membrane.
[0151] The hydrophilic, composite, microporous membrane disposed,
for instance, immediately upstream of a site of washing
semiconductors, etc., can remove even a trace amount of impurities
from ultra-pure water, improving the production yield of
semiconductors. Also, even when the hydrophilic, composite,
microporous membrane is disposed immediately upstream of a use
site, a booster pump is not needed, making it unnecessary to modify
the pressure resistance of pipes, etc., thereby lowering the
facility cost. When the hydrophilic, composite, microporous
membrane is disposed immediately upstream of a use site, it is
preferably charged into a case to form a flat filtration membrane
module.
[0152] Because the hydrophilic, composite, microporous membrane has
affinity for anions and cations, it can exhibit excellent
properties in such applications as electrolytic polymer membranes
for fuel cells, separators for nickel hydrogen batteries, etc.
Though properly determined depending on applications, the thickness
of the hydrophilic, composite, microporous membrane is usually 5 to
200 .mu.m, preferably 5 to 100 .mu.m when used as a water treatment
membrane.
[0153] This invention will be described in more detail with
reference to Examples below without intention of restricting the
scope of this invention.
Example 1
(1) Production of Microporous Polyethylene Membrane
[0154] 100 parts by mass of a polyethylene (PE) composition
comprising 20% by mass of ultra-high-molecular-weight polyethylene
(UHMWPE) having a mass-average molecular weight (Mw) of
2.0.times.10.sup.6 and a molecular weight distribution (Mw/Mn) of
8, and 80% by mass of high-density polyethylene (HDPE) having Mw of
3.5.times.10.sup.5 and Mw/Mn of 13.5 was dry-blended with 0.375
parts by mass of
tetrakis[methylene-3-(3,5-ditertiary-butyl-4-hydroxyphenyl)-propionate]
methane. Measurement revealed that the PE composition comprising
UHMWPE and HDPE had Mw/Mn of 16, a melting point of 135.degree. C.,
and a crystal dispersion temperature of 100.degree. C.
[0155] The Mws and Mw/Mn ratios of UHMWPE and HDPE were measured by
a gel permeation chromatography (GPC) method under the flowing
conditions (the same conditions applied below).
[0156] Measurement apparatus: GPC-150C available from Waters
Corporation,
[0157] Column: Shodex UT806M available from Showa Denko K.K.,
[0158] Column temperature: 135.degree. C.,
[0159] Solvent (mobile phase): o-dichlorobenzene,
[0160] Solvent flow rate: 1.0 ml/minute,
[0161] Sample concentration: 0.1% by mass (dissolved at 135.degree.
C. for 1 hour),
[0162] Injected amount: 500 .mu.l,
[0163] Detector: Differential Refractometer available from Waters
Corp., and
[0164] Calibration curve: Produced from a calibration curve of a
single-dispersion, standard polystyrene sample using a
predetermined conversion constant.
[0165] 25 parts by mass of the resultant PE composition was charged
into a double-screw extruder (inner diameter=58 mm, L/D=42), and 75
parts by mass of liquid paraffin was supplied to the double-screw
extruder via its side feeder. Melt blending was conducted at
210.degree. C. and 200 rpm to prepare a polyethylene solution in
the extruder. This polyethylene solution was supplied from the
double-screw extruder to a T-die, extruded therefrom in a
2.0-mm-thick sheet, and cooled by a cooling roll controlled at
40.degree. C. to form a gel-like sheet.
[0166] The gel-like sheet was simultaneously biaxially stretched by
a continuous stretching machine to 5-fold in both MD and TD at
119.5.degree. C. The stretched gel-like sheet was immersed in a
washing bath of methylene chloride controlled at 25.degree. C., and
continuously washed. The washed membrane was air-dried at room
temperature and taken by a reel. The resultant membrane was
stretched again by a continuous stretching machine to 1.4-fold in
TD at a speed of 15%/second and at a temperature of 110.degree. C.
The re-stretched membrane was fixed to a tenter, and heat-set at a
temperature of 110.degree. C. for 30 seconds to form a microporous
polyethylene membrane. The properties of the microporous
polyethylene membrane were an average thickness of 31.0 .mu.m, air
permeability of 85 sec/100 ml/20 .mu.m, a porosity of 63.5%, an
average pore size of 0.085 .mu.m, and pin puncture strength of 240
gf/20 .mu.m. The measurement methods of the properties were as
follows (the same is applicable below).
[0167] (a) Average Thickness (.mu.m)
[0168] The thickness of the microporous polyethylene membrane was
measured at a 5-mm interval over a width of 30 cm by a contact
thickness meter, and the measured thickness was averaged.
[0169] (b) Air Permeability (sec/100 cm.sup.3/20 .mu.m)
[0170] The air permeability P.sub.1 of the microporous polyethylene
membrane having a thickness T.sub.1 was measured according to JIS
P8117, and converted to air permeability P.sub.2 at a thickness of
20 .mu.m by the formula of
P.sub.2.dbd.(P.sub.1.times.20)/T.sub.1.
[0171] (c) Porosity (%)
[0172] It was measured by a mass method.
[0173] (d) Pin Puncture Strength (mN/20 .mu.m)
[0174] The maximum load was measured when a microporous membrane
having a thickness T.sub.1 was pricked with a needle of 1 mm in
diameter with a spherical end surface (radius R of curvature: 0.5
mm) at a speed of 2 mm/second. The measured maximum load L.sub.a
was converted to the maximum load L.sub.b at a thickness of 20
.mu.m by the formula of L.sub.b=(L.sub.a.times.20)/T.sub.1, which
was regarded as pin puncture strength.
[0175] (2) Graft Polymerization with Glycidyl Methacrylate
[0176] Fixed to an aluminum frame plate of 30 cm.times.30 cm, the
microporous polyethylene membrane was immersed in hexane for
washing, and dried. Using an electron accelerator (acceleration
voltage: 3.0 MeV, and electron beams current: 5 mA), the dried
membrane was irradiated with electron beams of 80 kGy in a nitrogen
atmosphere. The membrane fixed to the frame plate was immersed in a
deoxidized 1-%-by-mass solution of glycidyl methacrylate in
methanol to conduct graft polymerization at 50.degree. C. for 30
minutes, washed with methanol, and dried. A graft ratio calculated
from the mass change of the membrane per a unit area before and
after the graft polymerization was 20% by mass per 100% by mass of
the ungrafted microporous polyethylene membrane, which was 1.4
milliequivalent/g as the glycidyl group.
[0177] (3) Introduction of Tertiary Amino Group
[0178] The membrane graft-polymerized with glycidyl methacrylate,
which was fixed to the frame, was immersed in a 10-%-by-mass
solution of dimethylamine in an IPA/water mixed solvent (IPA/water
mass ratio=11.1/88.9), to conduct the addition reaction of amine to
the epoxy group at a temperature of 50.degree. C. for 1 hour, and
then washed with pure water. Part of this membrane was immersed in
1-N sodium hydroxide to turn the dimethylamino group to an OH
group, washed with pure water, dried, and reacted with 1-N
hydrochloric acid. The titration of consumed HCl with an alkali
until neutralization revealed that the amount of amine introduced
was 0.5 milliequivalent/g as the glycidyl group.
[0179] (4) Introduction of Sulfonic Acid Group
[0180] The dimethylamino-group-introduced membrane was immersed in
a solution of sodium sulfite in an IPA/water mixed solvent, to
react the unreacted epoxy group with sodium sulfite at a
temperature of 80.degree. C. for 15 hours. The resultant membrane
was washed with pure water, immersed in 1-N hydrochloric acid to
cause ion exchange from sodium to H to form a sulfonic acid group,
washed with pure water, and dried. Infrared spectrum confirmed that
the sulfonic acid group was introduced into the membrane. Assuming
that the sulfonic acid group was completely introduced into the
unreacted epoxy group, the amount of the sulfonic acid group
introduced was 0.9 milliequivalent/g as the glycidyl group.
[0181] (5) Conversion Reaction to Quaternary Amino Group
[0182] The microporous polyethylene membrane, into which a
dimethylamino group and a sulfonic acid group were introduced, was
immersed in a 10-%-by-mass solution of benzyl chloride in IPA at a
temperature of 80.degree. C. for 15 hours, to turn the
dimethylamino group to a quaternary one. The treated membrane was
sufficiently washed with pure water, and dried to obtain a
hydrophilic, composite, microporous membrane having a quaternary
amino group and a sulfonic acid group.
[0183] (6) Properties
[0184] The resultant hydrophilic, composite, microporous membrane
had an average thickness of 32.3 .mu.m, air permeability of 110
sec/100 ml/20 .mu.m, a porosity of 59.5%, and pin puncture strength
of 220 gf/20 .mu.m.
Comparative Example 1
[0185] A hydrophilic, composite, microporous membrane was produced
in the same manner as in Example 1 except for introducing only a
sulfonic acid group into the microporous polyethylene membrane.
Comparative Example 2
[0186] A hydrophilic, composite, microporous membrane was produced
in the same manner as in Example 1 except for introducing only a
quaternary amino group into the microporous polyethylene
membrane.
Comparative Example 3
[0187] The membranes of Comparative Examples 1 and 2 were laminated
to produce a hydrophilic, composite, microporous membrane.
[0188] Each hydrophilic, composite, microporous membrane of 5
cm.times.5 cm obtained in Example 1 and Comparative Examples 1 to 3
was charged into a case to produce a flat filtration membrane
module, and its water permeability and filtering properties
(properties of removing fine silica particles, anions and metal
ions) was measured by the following methods using water containing
the components shown in Table 1. The results are shown in Table
2.
TABLE-US-00001 TABLE 1 Components in Water Fine Silica
Particles.sup.(1) (/ml).sup.(2) 100 Anions.sup.(3) NO.sub.3.sup.-
(ppb) 16 SO.sub.4.sup.2- (ppb) 9 Cl.sup.- (ppb) 29 Metal
Ions.sup.(4) Na Ion (ppb) 11 Ca Ion (ppb) 7 Fe Ion (ppb) 7 Cu Ion
(ppb) 6 Note: .sup.(1)Particle size of less than 0.1 .mu.m.
.sup.(2)The concentration was measured by a particle counter.
.sup.(3)After concentrated, water was qualitatively and
quantitatively measured by ion chromatography.
.sup.(4)Qualitatively and quantitatively measured by an ICP-MS
method.
[0189] (a) Water Permeation Speed (L/hr/m.sup.2/atm)
[0190] 1 L of water was caused to pass through the flat filtration
membrane module at room temperature and a pressure of 50.54 kPa
(380 mmHg) to measure the time taken for water to pass through
(water permeation time). The water permeation speed was determined
by the following equation:
Water permeation speed(L/hr/m.sup.2/atm)=amount of water
passed(L)/time(hr)/membrane size(m.sup.2)/pressure(atm).
[0191] (b) Measurement of Concentration of Fine Silica
Particles
[0192] Water was caused to pass through the flat filtration
membrane module under the above conditions, and the concentration
(/ml) of fine silica particles was measured by a particle counter
before and after filtration.
[0193] (c) Measurement of Anion Concentrations
[0194] Water was caused to pass through the flat filtration
membrane module under the above conditions, and water was
concentrated before and after filtration. Anions were qualitatively
and quantitatively measured by an ICP-MS (inductively coupled
plasma mass spectroscopy) method, and the concentrations (ppb) of
anions were expressed as those of the unconcentrated water.
[0195] (d) Measurement of Concentrations of Metal Ions
[0196] Water was caused to pass through the flat filtration
membrane module under the above conditions, and metal ions were
qualitatively and quantitatively measured by the ICP-MS method
before and after filtration to determine the concentrations (ppb)
of metal ions.
TABLE-US-00002 TABLE 2 No. Example Comparative Comparative
Comparative 1 Example 1 Example 2 Example 3 Properties Of
Hydrophilic, Composite Microporous Membrane Quaternary Amino Group
Yes No Yes Yes (0.5 ME/g).sup.(1) Sulfonic Acid Group Yes Yes No
Yes (0.9 ME/g).sup.(2) Average Thickness (.mu.m) 32.3 33 31.8 63.5
Air Permeability 110 -- -- -- (sec/100 cm.sup.3/20 .mu.m) Porosity
(%) 59.5 -- -- -- Pin Puncture Strength 220 -- -- -- (gf/20 .mu.m)
Water Permeability and Filtration Properties of Hydrophilic,
Composite Microporous Membrane Water Permeation Speed 820 790 810
220 (L/hr/m.sup.2/atm) Components in Treated water Fine Silica
Particles.sup.(3) (/ml).sup.(4) <5 <5 <5 <5
Anions.sup.(5) NO.sub.3.sup.- (ppb) <0.1 15 <0.1 <0.1
SO.sub.4.sup.2- (ppb) <0.1 10 <0.1 <0.1 Cl.sup.- (ppb)
<0.1 30 <0.1 <0.1 Metal Ions.sup.(6) Na Ion (ppb) <0.1
<0.1 10 <0.1 Ca Ion (ppb) <0.1 <0.1 6 <0.1 Fe Ion
(ppb) <0.1 <0.1 6 <0.1 Cu Ion (ppb) <0.1 <0.1 6
<0.1 Note: .sup.(1)Measured value (unit: milliequivalent/g),
which was converted to the amount of the glycidyl group.
.sup.(2)Theoretical value (unit: milliequivalent/g), which was
converted to the amount of the glycidyl group. .sup.(3)Particle
size: less than 0.1 .mu.m. .sup.(4)The concentration was measured
by a particle counter. .sup.(5)After concentrated, the filtrated
water was qualitatively and quantitatively measured by ion
chromatography. .sup.(6)Qualitatively and quantitatively measured
by the ICP-MS method.
[0197] As is clear from Table 2, the hydrophilic, composite,
microporous membrane of Example 1, though being as thin as 32.3
.mu.m, was excellent in all of the pin puncture strength, the water
permeability, the fine-particles-removing properties, the
anion-removing properties and the cation-removing properties. On
the other hand, the membrane of Comparative Example 1, which did
not have any one of primary to quaternary amino groups, had no
anion-removing properties. The membrane of Comparative Example 2,
which did not have a sulfonic acid group, had no cation-removing
properties. The membrane of Comparative Example 3, which was as
thick as substantially 2-fold of the membrane of Example 1, had
much poorer water permeability.
Example 2
[0198] (1) Graft Polymerization with Glycidyl Methacrylate
[0199] The same microporous polyethylene membrane as in Example 1
was washed, dried, and irradiated with electron beams in the same
manner as in Example 1. The irradiated membrane was
graft-polymerized with GMA in the same manner as in Example 1
except that the treatment time was 15 minutes. Part of the membrane
was cut out, washed with methanol, and dried. The measurement of
mass change per a unit area before and after graft polymerization
revealed that the graft ratio was 11% by mass per 100% by mass of
the ungrafted, microporous polyethylene membrane. This graft ratio
was converted to the amount of the glycidyl group, which was 0.77
milliequivalent/g.
[0200] (2) Graft Polymerization with Methacrylic Acid
[0201] The membrane graft-polymerized GMA was immersed in a
1-%-by-mass solution of methacrylic acid in methanol at 50.degree.
C. for 40 minutes for graft polymerization. Part of the membrane
was cut out, washed with methanol, and dried. The measurement of
mass change per a unit area before and after graft polymerization
revealed that the graft ratio of the methacrylic acid was 11% by
mass per 100% by mass of the ungrafted, microporous polyethylene
membrane. This graft ratio was converted to the amount of the
carboxyl group, which was 0.83 milliequivalent/g.
[0202] (3) Introduction of Tertiary Amino Group
[0203] The carboxyl-group-introduced membrane was immersed in a
110-%-by-mass solution of dimethylamine in an IPA/water mixed
solvent (IPA/water mass ratio 11.1/88.9) at a temperature of
50.degree. C. for 1 hour to cause the addition reaction of amine to
the epoxy group, and washed with pure water. Part of this membrane
was immersed in 1-N sodium hydroxide to turn the dimethylamino
group to OH, washed with pure water, and dried. Reacted with 1-N
hydrochloric acid, the amount of HCl consumed was titrated with an
alkali to determine the amount of amine introduced. The amount of
dimethylamino group was 0.70 milliequivalent/g.
[0204] (4) Conversion Reaction to Quaternary Amino Group
[0205] The microporous polyethylene membrane, into which a
dimethylamino group and a carboxyl group were introduced, was
immersed in a 10-%-by-mass solution of benzyl chloride in IPA at a
temperature of 80.degree. C. for 15 hours to turn the dimethylamino
group to a quaternary one. The resultant membrane was washed with
pure water, and dried to obtain a hydrophilic, composite,
microporous membrane having a quaternary amino group and a carboxyl
group. This hydrophilic, composite, microporous membrane had an
average thickness of 33.5 .mu.m, air permeability of 120 sec/100
ml/20 .mu.m, a porosity of 58.5%, and pin puncture strength of 225
gf/20 .mu.m.
Example 3
[0206] A microporous polyethylene membrane having a quaternary
amino group in an amount of 0.68 milliequivalent/g (converted to
the dimethylamino group) was produced in the same manner as in
Example 2 except that methacrylic acid was not grafted. The
resultant quaternary-amino-group-containing, microporous
polyethylene membrane was exposed to a plasma gas generated at an
output of 1.5 kW in an argon atmosphere while being conveyed by a
roll at a speed of 0.3 m/min, to form a hydrophilic, composite,
microporous membrane having a carboxyl group. Infrared spectrum
measurement revealed an absorption peak at 1,720 cm.sup.-1,
confirming that the carboxyl group was introduced into the
hydrophilic, composite, microporous membrane.
Comparative Example 4
[0207] A hydrophilic, composite, microporous membrane was produced
in the same manner as in Example 2 except that only a carboxyl
group was introduced into the microporous polyethylene
membrane.
Comparative Example 5
[0208] A hydrophilic, composite, microporous membrane was produced
in the same manner as in Example 2, except that only a quaternary
amino group was introduced into the microporous polyethylene
membrane.
Comparative Example 6
[0209] The membranes of Comparative Examples 4 and 5 were laminated
to produce a hydrophilic, composite, microporous membrane.
[0210] Each hydrophilic, composite, microporous membrane of 5
cm.times.5 cm obtained in Examples 2 and 3 and Comparative Examples
4 to 6 was charged into a case to produce a flat filtration
membrane module, and subjected to a water permeability test and a
filtration test under the same conditions as above except for using
water having the components shown in Table 3. The results are shown
in Table 4.
TABLE-US-00003 TABLE 3 Components in Water Fine Silica
Particles.sup.(1) (/ml).sup.(2) 100 Anions.sup.(3) SO.sub.4.sup.2-
(ppb) 9 Cl.sup.- (ppb) 20 Metal Ions.sup.(4) Ca Ion (ppb) 11 Cu Ion
(ppb) 6 Note: .sup.(1)-(4)Same as in Table 1.
TABLE-US-00004 TABLE 4 No. Example 2 Example 3 Properties Of
Hydrophilic, Composite Microporous Membrane Quaternary amino group
Yes Yes (0.70 ME/g).sup.(1) (0.68 ME/g).sup.(1) Carboxyl group Yes
Yes.sup.(3) (0.83 ME/g).sup.(2) Average Thickness (.mu.m) 33.5 31.7
Air Permeability 120 -- (sec/100 cm.sup.3/20 .mu.m) Porosity (%)
58.5 -- Pin Puncture Strength 225 -- (gf/20 .mu.m) Water
Permeability and Filtration Properties of Hydrophilic, Composite
Microporous Membrane Water Permeation Speed 860 780
(L/hr/m.sup.2/atm) Components in Treated water Fine Silica
Particles.sup.(4) (/ml).sup.(5) <5 <5 Anions.sup.(6)
SO.sub.4.sup.2- (ppb) <0.1 <0.1 Cl.sup.- (ppb) <0.1
<0.1 Metal Ions.sup.(7) Ca Ion (ppb) 3 4 Cu Ion (ppb) 2 4 No.
Comparative Comparative Comparative Example 4 Example 5 Example 6
Properties Of Hydrophilic, Composite Microporous Membrane
Quaternary amino group No Yes Yes Carboxyl group Yes.sup.(3) No
Yes.sup.(3) Average Thickness (.mu.m) 31.5 32.1 62.8 Air
Permeability -- -- -- (sec/100 cm.sup.3/20 .mu.m) Porosity (%) --
-- -- Pin Puncture Strength -- -- -- (gf/20 .mu.m) Water
Permeability and Filtration Properties of Hydrophilic, Composite
Microporous Membrane Water Permeation Speed 740 820 240
(L/hr/m.sup.2/atm) Components in Treated water Fine Silica
Particles.sup.(4) (/ml).sup.(5) <5 <5 <5 Anions.sup.(6)
SO.sub.4.sup.2- (ppb) 9 <0.1 <0.1 Cl.sup.- (ppb) 20 <0.1
<0.1 Metal Ions.sup.(7) Ca Ion (ppb) 4 11 2 Cu Ion (ppb) 3 6 2
Note: .sup.(1)Measured value (converted to the amount of
dimethylamino group). .sup.(2)Theoretical value (converted to the
amount of carboxyl group). .sup.(3)An absorption peak was detected
at 1,720 cm.sup.-1 in infrared spectrum. .sup.(4)Particle size:
less than 0.1 .mu.m. .sup.(5)The concentration was measured by a
particle counter. .sup.(6)After concentrated, the filtrated water
was qualitatively and quantitatively measured by ion
chromatography. .sup.(7)Qualitatively and quantitatively measured
by the ICP-MS method.
[0211] As is clear from Table 4, the hydrophilic, composite,
microporous membrane of Example 2 was as thin as 33.5 .mu.m, and
had excellent pin puncture strength. The hydrophilic, composite,
microporous membranes of Examples 2 and 3 were excellent in all of
water permeability, fine-particles-removing properties,
anion-removing properties and cation-removing properties. On the
other hand, the membrane of Comparative Example 4, which did not
contain any one of primary to quaternary amino groups, had no
anion-removing properties. The membrane of Comparative Example 5
containing no carboxyl group did not have cation-removing
properties. The membrane of Comparative Example 6, which was as
thick as substantially 2-fold of Examples 2 and 3, had much poorer
water permeability.
EFFECT OF THE INVENTION
[0212] The hydrophilic, composite, microporous membranes of this
invention having excellent water permeability, mechanical strength,
fine-particles-removing properties, anion-removing properties and
cation-removing properties are suitable as reverse osmosis
filtration membranes, ultrafiltration membranes, microfiltration
membranes, etc. for treating water. According to the production
method of this invention, a good balance of an anion exchange group
and a cation exchange group can be added onto the outer surface and
pore surface of the microporous, thermoplastic resin membrane.
* * * * *